Requirement of inner cell mass for efficient chorionic gonadotrophin secretion by blastocysts of common marmosets (Callithrix jacchus).

The role of the inner cell mass in the induction of chorionic gonadotrophin synthesis and secretion by the trophoblast of the peri-implantation primate blastocyst was studied in common marmoset monkeys. An in vitro system for the culture of blastocysts commencing with blastocysts collected 8 days after conception was developed. Chorionic gonadotrophin measured in the spent culture fluid was first detected in most blastocysts after 3 or 4 days (day 11 or 12) of culture at a time equivalent to implantation in vitro. Initial secretion of chorionic gonadotrophin coincided with development of parietal endoderm and histological appearance of syncytiotrophoblast in the polar trophoblast. Little chorionic gonadotrophin was secreted by blastocysts with a poorly developed, or absent, inner cell mass. Mural trophoblast removed from blastocysts after 2 days of culture (day 10) grew in vitro as a unilaminar vesicle but failed to secrete significant amounts of chorionic gonadotrophin. However, mural trophoblast from older blastocysts (days 13 and 14) after chorionic gonadotrophin secretion had commenced continued to secrete chorionic gonadotrophin, with trophoblast from day 14 blastocysts secreting significantly more than that from day 13. It was concluded from these studies that while mural trophoblast from marmoset blastocysts will proliferate in vitro in the absence of an inner cell mass, efficient induction of chorionic gonadotrophin secretion requires the presence of the inner cell mass or its derivatives. Once chorionic gonadotrophin secretion has commenced, secretion will continue in the absence of the inner cell mass.